GaN-based light-emitting diodes (LEDs) have been popular recently. Sapphire is the most commonly used substrate in the epitaxy growth of LED devices, but limits the devices performance due to its poor electrical and thermal conductivity. Ultraviolet (UV) laser lift-off (LLO) technology has been developed for transferring GaN LED thin films from a sapphire substrate to a Si or Cu substrate without degrading the crystal quality. Two common issues with LLO procedures are incomplete decomposition at the chip edges and partitioning the diced chip into smaller regions.
Chips, notches, polishing imperfections, and the optical effects at the sapphire boundaries may cause incomplete decomposition locally within the LLO layer. Upon separation of the substrate and film, this may cause film damage, especially cracking.
Patterning the LLO region into portions smaller than the diced piece may often be desired. The typical method for doing this is by patterning and etching through the LED to the sapphire substrate to partition the intended LLO regions prior to dicing. Many techniques use a wet or plasma etching process employing a photolithography step to partition LLO regions.